Of great benefit, but not limited to seafloor mineral exploration, is a technique that fairly rapidly determines the composition of a drilled vibracore (in a time comparable to the time involved in obtaining the core). The rapid assessment is desired to predict whether a given region warrants further exploration by coring. A proposed monitoring system, based on neutron capture gamma ray analysis, consists of a container tank filled with water and tubular extensions that house a Cf-252 neutron source and a detector positioned within the tank. The core sample is passed through the system in stop and count steps. The net count rates, due to "signature" capture gamma rays from neutron capture in elements in the core sample, are proportional to the amount of the element responsible for emitting the capture gamma ray. The proposed system was modeled and simulated by the Monte Carlo method to predict the relationship between the response of the detector and the elemental concentrations within the sample. Accurate and detailed treatment of neutron transport and gamma ray production and attenuation within the system were employed not only to predict the relationship of the photopeak responses with respect to elemental concentrations, but also to permit investigation of the design parameters and structural material changes in the system. The developed Monte Carlo code utilizes a variety of variance reduction techniques, such as implicit absorption with Russian Roulette and deterministic production of the gamma rays of interest, along with a form of correlated sampling to predict simultaneously the responses over a range of interest of the elemental concentrations. The predicted results were compared with predictions obtained from a well established general purpose Monte Carlo code (MCNP). / Graduation date: 1990

Excited states in the transitional nucleus 160Yb have been studied using gamma-ray and conversion electron spectroscopy following the beta+/EC decay of 160Lu. Excited states in the nuclei 160Tm and 160Er have been studied following the beta+/EC decay of 160Yb and 160Tm, respectively. The data for the present study were obtained at TRIUMF in Vancouver, Canada at the ISAC-1 facility through radioactive sources moved into the combination of the 8pi gamma-ray spectrometer array and the Pentagonal Array for Conversion Electron Spectroscopy (PACES). Analysis of gamma-ray gated gamma-ray, gamma-ray gated conversion electron and conversion electron gated gamma-ray spectra resulted in the discovery of a new first excited state and the establishment of a level scheme for 160Tm which differs from the one adopted; as well as a test of the rotational characteristics of 160Er with intensity comparisons to both the spin-5 beta-decaying isomer study of by Singh et al. and the spin-parity 1- beta decay study of by Strusny et al. and Bykov et al.

This work presents two research efforts, one involving planetary science education research and a second involving the surface composition of Mars. In the former, student beliefs and reasoning difficulties associated with the greenhouse effect were elicited through student interviews and written survey responses from >900 US undergraduate non-science majors. This guided the development of the Greenhouse Effect Concept Inventory (GECI), an educational research tool designed to assess pre- and post-instruction conceptual understanding of the greenhouse effect. Three versions of this multiple-choice instrument were administered to >2,500 undergraduates as part of the development and validation process. In contrast to previous research efforts regarding causes, consequences, and solutions to the enhanced greenhouse effect, the GECI focuses primarily on the physics of energy flow through Earth's atmosphere. The GECI is offered to the science education community as a research tool for assessing instructional strategies on this topic.It was confirmed that the study population subscribes to several previously identified beliefs. These include correct understandings that carbon dioxide is an important greenhouse gas and the greenhouse effect increases planetary surface temperatures. Students also commonly associate the greenhouse effect with increased penetration of sunlight into and trapping of solar energy in the atmosphere. Students intermix concepts associated with the greenhouse effect, global warming, and ozone depletion. Reinforcing the latter concept, a majority believe that the Sun radiates most of its energy as ultraviolet light. Students also describe inaccurate and incomplete trapping models, which include permanent trapping, trapping through reflection, and trapping of gases and pollution. Another reasoning difficulty involves the idea that Earth's surface radiates energy primarily during the nighttime.The second research effort describes the distribution of chlorine on Mars measured by the Mars Odyssey Gamma Ray Spectrometer (GRS). The distribution of chlorine is heterogeneous across the surface, with a concentration of high chlorine centered over the Medusa Fossae Formation. The distribution of chlorine correlates positively with hydrogen and negatively with silicon and thermal inertia. Four mechanisms (aeolian, volcanic, aqueous, and hydrothermal) are discussed as possible factors influencing the distribution of chlorine measured within the upper few tens of centimeters of the surface.

No description available.

<p>Two separate experimental searches for second-order weak nuclear decays to excited final states were conducted. Both experiments were carried out at the Kimballton Underground Research Facility to provide shielding from cosmic rays. The first search is for the two-neutrino double-beta decay of 96Zr to excited final states of the daughter nucleus, 96Mo. As a by product of this experiment, the beta decay of 96Zr was also investigated. Two coaxial high-purity germanium detectors were used in coincidence to detect gamma rays produced by the daughter nucleus as it de-excited to the ground state. After collecting 1.92 years of data with 17.91 g of enriched 96Zr, half-life limits at the level of 10^20 yr were produced. Measurements of this decay are important to test neutrinoless double-beta decay nuclear matrix element calculations, which are necessary to extract the neutrino mass from a measurement of the neutrinoless double-beta decay half-life. </p><p>The second experiment is a search for the resonantly-enhanced neutrinoless double-electron capture decay of 156Dy to excited states in 156Gd. Double-electron capture is a possible experimental alternative to neutrinoless-double beta decay, which could distinguish the Dirac or Majorana nature of the neutrino. Two clover high-purity germanium detectors were used in coincidence to investigate the decay. A 213.5 mg enriched 156Dy sample was observed for 0.635 year, producing half-life limits of 10^17 yr. The limits produced by both of these experiments are currently the most stringent limits available for these decays.</p> / Dissertation

The seabed is envisaged to meet the increased future demands for minerals from the rapidly growing industrialized societies of the world. Shipboard analysis of cores can significantly reduce the cost and time spent at the exploratory drilling stage by obviating the need to go back to land for analysis. It can further speed the exploration process by enabling a quick modification of the exploration plan based on the results of the shipboard analysis. A ²⁵²Cf-based analyzer utilizing the prompt gamma neutron activation analysis technique has been designed. The analyzer is a spherical iron shell with the source at its center. The seabed core is passed through a hollow composite tube which is positioned a short distance directly below the source and the resulting prompt gamma rays are collimated to a HPGe detector. The rest of the sphere is filled with paraffin. The gamma ray flux at the detector is converted into a count rate by using a semi-empirical detector response function. This count rate data are then used to determine the sensitivity and detection limits for the chosen elements (Mg, Al, Ti, Cr, Mn, Fe, Ni and Cu). Monte Carlo simulations using the Monte Carlo neutron photon coupled transport code, MCNP, were carried out for a parametric study of important variables influencing the design of the analyzer. These parameters included the moderator type, source to sample distance and sample porosity. MCNP was then used to model the analyzer and to generate the neutron flux profiles in the sample and the prompt gamma flux at the detector. Due to the non-availability of the prompt gamma data for most of the elements of economic interest in the ENDF/B-V cross section libraries associated with MCNP, the point kernel photon transport code ISOSHLD-II (modified for high energy gamma rays) was used to generate the gamma flux at the detector for specific elements. The ISOSHLD-II source term was calculated based on known gamma production data (thermal capture only) and the thermal neutron flux in the sample obtained from MCNP computations. The sensitivity and detection limits obtained from the isotopic source based analyzer were compared for the case of aluminum with values reported from reactor facilities. The results obtained indicate that the analyzer designed in this work could prove suitable for the on-line analysis of many elements of economic interest in seabed cores at the 1 weight percent level. / Graduation date: 1992

Neste trabalho são apresentados os resultados obtidos do estudo da estrutura do núcleo \'ANTPOT. 58 CO\' utilizando a técnica de espectroscopia de raios gama em linha. Este núcleo foi produzido a partir da reação de fusão-evaporação \'ANTPOT. 51 V\'(ANTPOT. 10 B\', p2n), com energia de feixe de 33 MeV incidindo em três alvos de 200\'mü\'g/\'cm POT. 2\', realizada no acelerador Pelletron da Universidade de São Paulo. Foram feitas medidas em coincidência \'gama\'\'gama\'-partícula com o espectrômetro de raios \'gama\' Saci-Pererê, composto de 4 detectores de GeHP com blindagem Compton, e um sistema auxiliar para detectar partículas carregadas, consistindo de 11 telescópios cintiladores \'delta\'E-E tipo phoswich. Foram encontradas quarenta e sete transições novas que depopulam trinta e sete novos estados. O esquema de níveis proposto foi estendido até uma energia de excitação de 8 MeV e momento angular de \'J POT. pi\'=\'11 POT. +\'. A atribuição dos valores de spins foi baseada na razão DCO (Correlação Direcional de Estados Orientados). Os resultados experimentais foram comparados com os calculados pelo Modelo de Camadas em Larga Escala (LSSM) utilizando os códigos MSHELL e Antoine, assim como a interação residual GXPF1, desenvolvida para ser usada na camada pf Foram interpretados dezenove estados excitados a partir do LSSM. Foram medidas também as vidas médias para treze estados excitados do \'ANTPOT. 58 CO\' utilizando o Método de Deslocamento Doppler Atenuado (DSAM). Para este estudo, o núcleo \'ANTPOT. 58 CO\' foi produzido a partir da reação \'ANTPOT. 51 V\'(ANTPOT. 10 B\', p2n) com energia de feixe de 36 MeV, usando um alvo de 770\'mü\'g/\'cm POT. 2\' prensado em um suporte de Pb. Os valores experimentais também foram comparados aos cálculos do LSSM. Probabilidades de transição reduzidas B(Ml), e portanto as vidas médias, foram bem reproduzidas pelo modelo teórico para cinco níveis identificados. Os níveis de energia observados apresentaram funções de onda com grande mistura de configurações sendo a principal dada por \'pi\'\'f POT -1 IND. 7/2\' (PRODUTO VETORIAL) v \'p POT 2 IND. 3/2\' \'f POT 1 IND. 5/2\',. Os resultados indicam que a maior parte dos estados excitados do núcleo \'ANTPOT. 58 CO\' tem um comportamento esférico e são bem reproduzidos considerando excitações de partícula única / The excited states in the doubly odd nucleus \'ANTPOT. 58 CO\' have been studied using inbeam gama-ray spectroscopy. The \'ANTPOT. 58 CO\' nucleus has been produced with the fusionevaporation reaction \'ANTPOT. 51 V\'(ANTPOT. 10 B\', p2n) at 33 MeV bombarding energy, using the SMV Pelletron accelerator of the University of São Paulo. Gamrna-gamma-charged particle coincidences were measured with the Saci-Pererê gama-ray spectrometer composed of 4 Compton-suppressed GeHP and an ancillary charged-particle detector system composed of 11 plastic phoswich scintillator ~E-E telescopes. We have found 47 new gama-transitions de-populating 37 new excited states. A level scheme extending up to an excitation energy of about 8.0 MeV and spin \'J POT. pi\'=\'11 POT. +\' has been proposed. The spin assignments were based on the DCO (Directional Correlation from Oriented States) ratios. The experimental results were compared with Large Scale Shell Model (LSSM) calculations performed with the MSHELL and Antoine codes using the GXPFl effective interaction, developed for use in the pf shell. We have interpreted 19 excited states in the frame of the LSSM. We have measured also the lifetimes for 13 excited states of the \'ANTPOT. 58 CO\' nucleus. The lifetimes were measured with the Doppler Shift Attenuation Method (DSAM). For this study the \'ANTPOT. 58 CO\' nuclei were populated with the reaction \'ANTPOT. 51 V\'(ANTPOT. 10 B\', p2n) at 36 MeV bombarding energy, using a target consisting of a 770\'mü\'g/\'cm POT. 2\' foil with Pb backing. The experimental values were also compared with the LSSM calculations. Experimental B(M1) reduced transition probabilities, and thus the lifetimes, are well reproduced by the theoretical model for fi v e o f the identified levels. The observed levels presented wave functions with large configuration mixing with the main configuration being \'pi\'\'f POT -1 IND. 1/2\' (PRODUTO VETORIAL) v \'p POT 2 IND. 3/2\' \'f POT 1 IND. 5/2\',. The results indicate that most of the excited states in the \'ANTPOT. 58 CO\' nucleus has a spherical behavior and is well reproduced considering single-particle excitations.

Philosophiae Doctor - PhD / Lying in a rapidly-changing transitional region between nuclei that may behave as spherical vibrators (N ≤ 88) or good rotors (N ≥ 92), the N = 90 isotones present a unique testing ground where new nuclear collective phenomena may be uncovered. As part of a general investigation of collective structures and the coupling of single-particle states to these structures, the 150Sm(12C,4nγγ) and 150Sm(13C,4nγγ) reactions at a beam energy of Elab = 65 MeV were used to study the low and medium spin structure of 158,159Er nuclei below spin 20~. The γ-γ coincidence events were detected in the nine escape-suppressed HPGe Clover detectors using the AFRODITE γ-ray spectrometer at the iThemba Laboratory for Accelerator Based Sciences. DCO ratios and γ-ray polarization measurements were used to establish the spins and parities of newly observed and confirm previously established rotational bands. The observed bands will be discussed in terms of both traditional quadrupole rotational-vibration models and recent predictions of octupole correlations in the N = 90 isotones and neighbouring nuclei. The data obtained will be compared with the spectroscopic systematics of neighbouring nuclei.

Philosophiae Doctor - PhD / Thoron Rn-220 is a radioactive gas with a half-life of 55.6 s. It has been identified as a possible health concern in specific places such as monazite processing plants and (rare-earth) mines. The short half-life of Rn-220 makes Rn-220 calibration sources and chambers less common than for the isotope Rn-222. There are many Rn-220 standard sources and chambers that are widely described in the literature and used for different applications and calibration. However, some of these chambers and sources are not easy to set up in typical nuclear environmental laboratories. In this project, we developed a Rn-220 standard source using a thorium nitrate solution (Th(NO3)4.6H2O). The solution was split into a large volume which was used in a Marinelli beaker to characterize its strength using a Hyper Pure Germanium (HPGe) detector, and a smaller volume of around 30 ml which was poured into a small bottle. The Rn-220 is extracted by bubbling air through the solution in the small bottle using an aerator. Gamma rays from the solution were measured simultaneously using a 76.2 mm × 76.2 mm NaI(Tl) detector. The gamma rays were measured for 66 hours. The accumulated spectra were thereafter analysed using an Excel spreadsheet where the counts in the Tl-208(2614 keV) peak were extracted and used to obtain the percentage of Rn-220 pumped out of the solution in the small bottle.

Philosophiae Doctor - PhD / Low- and medium-spin bands of 187Os have been studied using the AFRODITE array, following the 186W(4He,3n)187Os reaction at a beam energy of 37 MeV. The measurements of γ − γ coincidences, angular distribution ratios (RAD), polarization and γ-intensities were performed using eleven High Purity Germanium (HPGe) clover detectors. In the current work, all the previously known bands have been significantly extended and five new bands have been added to the level scheme. The observed bands are interpreted within the cranked shell model (CSM), cranked Nilsson-StrutinskyBogoliubov (CNSB) formalism and Quasiparticle-plus-Triaxial-Rotor (QTR) model. Systematic comparison of bands with the neighbouring isotopes has also been made. Comparison of the models with experimental data shows good agreement. The configurations of some of the previously observed bands have been modified. Most importantly, the coupling of 2+ γ band to the 11/2+[615] neutron configuration is observed for the first time.